The invention relates to a method of manufacturing a semiconductor device with a field effect transistor, in which method a semiconductor body is provided, at a surface, with a source region and a drain region, while using a doping mask containing a polycrystalline silicon (hereinafter referred to as poly), and in which method subsequently a dielectric layer is provided which is subjected to a material-removing treatment, such as etching or polishing, to remove a part of its thickness, so that the poly-containing doping mask is exposed again, whereafter said poly-containing doping mask is removed by means of a selective etch step and, subsequently, a conductive layer is provided in the resultant recess in the dielectric layer, which conductive layer constitutes the gate of the transistor. Such a method is known, inter alia, from the article "Sub-100 nm gate length metal gate NMOS transistors fabricated by a replacement gate process" by A. Chatterjee et. al., IEDM 97, pp. 821/824. The "replacement gate process" enables MOS transistors with a metal gate to be manufactured in a self-recording manner, instead of the customary polysilicon gates which have a much higher resistance.
In the known process, a dummy gate of polysilicon is formed in the same manner as the poly gate in standard CMOS processes. After the formation of the source and drain regions, an oxide layer which serves as the dielectric layer is deposited, whereafter the thickness of the dielectric layer is reduced down to the poly by means of chemico-mechanical polishing (hereinafter referred to as CMP). Subsequently, the poly of the dummy gate is removed by selective etching. The resultant recess in the oxide layer is filled by a metal gate of Al or W.
In practice it has been found that the reproducibility of this process is limited. In particular the point in time at which the chemico-mechanical polishing operation of the oxide layer is interrupted proved to be very critical. If the CMP is stopped too early, the remaining oxide makes it very difficult to remove the poly. If the CMP process is continued too long, then the height of the gate to be formed eventually proves to be ill-defined.